Appendix Fpppoe; Pppoe In Action; Benefits Of Pppoe; How Pppoe Works - ZyXEL Communications VSG-1200 User Manual

PPPoE in Action

An ADSL modem bridges a PPP session over Ethernet (PPP over Ethernet, RFC 2516) from your computer to an
ATM PVC (Permanent Virtual Circuit) which connects to an xDSL Access Concentrator where the PPP session
terminates (see the next figure). One PVC can support any number of PPP sessions from your LAN. PPPoE
provides access control and billing functionality in a manner similar to dial-up services using PPP.

Benefits of PPPoE

PPPoE offers the following benefits:
1. It provides you with a familiar dial-up networking (DUN) user interface.
2. It lessens the burden on the carriers of provisioning virtual circuits all the way to the ISP on multiple switches
for thousands of users. For GSTN (PSTN & ISDN), the switching fabric is already in place.
3. It allows the ISP to use the existing dial-up model to authenticate and (optionally) to provide differentiated
services.
Traditional Dial-up Scenario
The following diagram depicts a typical hardware configuration where the computers use traditional dial-up
networking.
Diagram 9 Single-computer per Modem Hardware Configuration

How PPPoE Works

The PPPoE driver makes the Ethernet appear as a serial link to the computer and the computer runs PPP over it,
while the modem bridges the Ethernet frames to the Access Concentrator (AC). Between the AC and an ISP, the
AC is acting as a L2TP (Layer 2 Tunneling Protocol) LAC (L2TP Access Concentrator) and tunnels the PPP
frames to the ISP. The L2TP tunnel is capable of carrying multiple PPP sessions.
With PPPoE, the VC (Virtual Circuit) is equivalent to the dial-up connection and is between the modem and the
AC, as opposed to all the way to the ISP. However, the PPP negotiation is between the computer and the ISP.
The VSG as a PPPoE Client
When using the VSG as a PPPoE client, the computers on the LAN see only Ethernet and are not aware of PPPoE.
This alleviates the administrator from having to manage the PPPoE clients on the individual computers.
PPPoE
VSG-1200 Vantage Service Gateway
Appendix F
PPPoE
U